Css rule appearing from some obscure place

I've created a child theme and have been making edits to the stylesheet via ftp. Somehow, an extra 40px of padding has been added to my navigation area that can not be overridden by my stylesheet, nor does it dissappear when I temporarily remove my stylesheet from my child theme folder. When I use firebug or Google Developer tools, I can see the 40px, and can temporarily disable it, but can not figure out the location of the file to permanently remove it. It seems to be located in some obscure place. Has this ever happened to you before?